2.3 Survey design
Plateau
pikas are social animals that usually live in low and open habitats, and
their young offspring often stay with the family in their birth year
since they are philopatric (Wang et al., 2020; Yu et al., 2017b).
Therefore, plateau pikas are territorial and patchy in a vast alpine
grassland. Because the diffusion of plateau pikas is a gradual process
(Pang et al., 2020b), it is easy to find sites without plateau pika
disturbance, even though these sites might be potentially suitable
habitats for plateau pikas.
A
stratified random and paired design was used to select the plots. At
each of the five sites, this study first selected 10 disturbed plots
where plateau pikas were present or active burrow entrances were
observed. These disturbed plots were 3 to 5 km from each other. Second,
a paired adjacent undisturbed plot without the presence of plateau pikas
and active burrow entrances was selected for each disturbed plot. The
distance between each disturbed plot and its paired undisturbed plot
ranged from 500 to 1000 m. If the distance between each disturbed plot
and its paired undisturbed plot was too close, plateau pikas could
possibly move from the disturbed plot to the undisturbed plot. To ensure
that each disturbed plot had a paired undisturbed plot to the greatest
extent, each paired plot was ensured to share the same alpine grassland,
with no obvious differences in soil types, topography or microclimate.
In total, there were 10 pairs of plots at each site and 100 plots across
five sites, including 50 disturbed plots and 50 undisturbed plots. The
size of each plot
was
35 m×35 m, similar to the average area of plateau pika’s home range of
1262.5 m2 (Fan et al., 1999).
Owing to grazing from mid-October to
early April, the litter in each plot was consumed by livestock, which
was better for estimating the aboveground biomass during the warm
season.